1. Field of the Invention
This invention relates generally to magnetic heads in disk drives, and more particularly to improved methods of making write coils of magnetic write heads as well as other structures with use of a ruthenium (Ru) seed layer for electroplating and a reactive ion etch (RIE) in ozone gas for seed removal.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) read head to form a merged MR head, certain elements of which are exposed at an air bearing surface (ABS). The write head comprises first and second pole pieces connected at a back gap that is recessed from the ABS. The first and second pole pieces have first and second pole tips, respectively, which terminate at the ABS. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces, and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for conducting write current through the coil layer which, in turn, induces write fields in the first and second pole pieces. A non-magnetic gap layer is sandwiched between the first and second pole tips. Write fields of the first and second pole tips at the ABS fringe across the gap layer. In a magnetic disk drive, a magnetic disk is rotated adjacent to, and a short distance (fly height) from, the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain information in the form of magnetized segments with fields detectable by the MR read head.
It is important to reduce the size of various structures within the magnetic head to achieve higher bit densities. One component of importance is the write coil, where the distance between each write coil layer (i.e. the “pitch”) has been reduced to 0.5 microns or less.
One conventional method of fabricating the write coil utilizes through-mask-plating (TMP), which is described in relation to FIGS. 10–11. In FIG. 10, a seed layer 1004 is deposited over a substrate and a plurality of write coil layers 1002 are formed over seed layer 1004. Seed layer 1004 is typically made of materials such as copper (Cu) or gold (Au). Write coil layers 1002 are typically copper (Cu) materials which have been electroplated with use of a patterned resist. For high aspect ratio structures, a problem arises when seed layer 1004 between each coil layer 1002 needs to be removed after the electroplating step.
One approach to remove seed layer 1004 between each coil layer 1002 is by ion milling, the result of which is shown in FIG. 11. After the ion milling, seed layer materials 1104 may not be fully removed and top portions of write coils 1102 may be damaged. Write coils 1102 may become electrically shorted. Note that it is difficult to etch the seed materials from the top of the structure in this manner, as the coil layers are relatively tall and the pitch between coil layers is narrow. With sputter etching (SE), the seed layer to be etched is immersed in a glow discharge where ions are accelerated across a sheath. Since the accelerated ions are not collimated, the process requires over-etching of the seed materials. The drawback to this approach is the increased depletion of the write coil thickness, which requires increasing the plating thickness of the write coils. Ion beam etching (IBE) is expected to have a tighter collimation of accelerated ions from a set of grids used to bias ions generated from confined plasma. Having a more efficient seed removal process, the IBE requires less over-etching of the seed materials. However, both SE and IBE approaches still have a number of shortcomings as the pitches are reduced. Namely, since the ejected species in both approaches are not inherently volatile, redeposition can occur and cause an electrical shorting of the write coils. Thus, since both techniques use purely physical processes to remove the seed materials, their selectivity is generally poor and over-etching tends to cause damage to the top coil structure and change the topography to the extent that it introduces more complications during subsequent fabrication steps.
Another conventional method of fabricating the write coil utilizes a damascene technique, which is described in relation to FIGS. 12–15. In FIG. 12, a dielectric structure 1202 such as a patterned resist is formed with a plurality of trenches. In FIG. 13, a thin seed layer 1302 is deposited over the entire dielectric structure 1202 including within the trenches. Damascene electroplating of copper (Cu) 1402 is then performed within the trenches and over dielectric structure 1202 in FIG. 14 to form a plurality of write coil layers. Next, a planarization process such as a chemical-mechanical polishing (CMP) is performed over the structure to remove top excess portions of the copper, to result in a write coil structure 1502 of FIG. 15.
This damascene technique of FIGS. 12–15 is useful in many situations. When the write coil's aspect ratio increases (i.e. the pitch between coil layers is reduced), however, the damascene technique has its limitations. For example, fabrication issues become more apparent when the pitch between coil layers is 0.5 microns or less. For one, the seed layer deposition becomes non-uniform. In addition, the damascene filling within the trenches is also non-uniform and voids (e.g. a void 1504 in FIGS. 14–15) remain within the structure after the electroplating. Furthermore, the damascene technique for such high aspect ratio structures is limited to metals which do not produce hydrogen evolution during electroplating; thus the technique is not applicable to magnetic materials which are used to form other structures within a magnetic head.
Accordingly, there is a resulting need for a method of fabricating write coils and other structures so as to overcome the deficiencies of the prior art.